Pavlovian conditioning researchers have displayed renewed interest in associations formed between two sensory events. Pairing of sensory events is also a central feature of a perceptual phenomenon described by McCollough in 1965, now known as the McCollough effect (ME). The proposal research is designed to integrate these two research traditions. The ME is demonstrated by presenting two chromatic grids during an "induction" period (e.g., a grid of black and green horizontal bars alternating with a grid of black and magenta vertical bars). Subsequently, complementary color aftereffects contingent on bar orientation are noted on an achromatic grid. For the above example, the white space between black horizontal bars appears pink and the white space between black vertical bars appears green. The ME is one of a category of contingent color aftereffects (CCAEs). The proposed research has two major objectives: (1) to evaluate the extent to which CCAEs, which result from pairing of color with another feature of the stimulus, can be understood as an instance of another well-studied phenomenon of pairing, Pavlovian conditioning, and (2) to study a new CCAE: illusory color seen on achromatic words following exposure to these words in color. In all experiments, a computer system is used for induction and assessment of CCAEs. Standard psychophysical procedures, appropriately modified for the task, are used to objectively assess aftereffect magnitude. The research concerning the contribution of Pavlovian conditioning to the CCAE will aid in understanding the contribution of learning to perception. Research addressed to the role of learning in the CCAE is also relevant to the role of learning in homeostatic functioning. Many conditioning phenomena typically studied with animals have been demonstrated with CCAEs, thus the research provides learning researchers with a valuable, in expensive alternative to the use of animals. The research concerning the word-CCAE may aid in understanding how people code and process the written word. In addition, it is likely that the word-CCAE research is relevant reports of troublesome contingent color aftereffects suffered by computer operators. These aftereffects have been implicated in ophthalmologic, psychiatric, and other work-related problems of computer operators.